In the November webpages you learned about habitats - places where plants and animals live. To fully understand how these plants and animals go about their daily lives within their habitats, we need to talk about something called an ecosystem. An ecosystem includes all the living organisms and non-living physical/chemical elements in a particular environment. The non-living elements may include such things as soil, rocks and water. When looking at an ecosystem, we are really interested in the relationships and interactions between living creatures and their environment.
There are usually several different types of ecosystems in a watershed. Because they live in water, fish live in aquatic ecosystems. Lakes, rivers, ponds and streams are all examples of aquatic ecosystems. Terrestrial ecosystems describe communities of plants and animals that live on dry land. As you have already learned, wetland systems are home to an amazing variety of fish and wildlife. Ecosystems are linked together by water and animals. Water may flow through a number of ecosystems on its way "from the mountains to the sea." An animal may make its home in one ecosystem and find food in another.
All living things, both plants and animals, need food or energy to survive. Energy enters an ecosystem in two ways. Green plants use water and the sun's energy to make their own food through a process called photosynthesis. Because of this ability, plants are called producers. Energy may also enter an ecosystem in the form of dead plant and animal material. For example, a leaf falls off a tree and enters a stream. The leaf is then consumed by small organisms called decomposers, primarily bacteria and fungi. Animals do not have the ability to make their own food and instead must eat plants or other animals. They are called consumers. Animals that eat other animals are called predators.
A food chain describes how energy is transferred from one organism to the next in an ecosystem. For example, a plant is eaten by an insect. The insect is then eaten by a frog which in turn is consumed by a snake. If you were to catch and eat the snake you would become a part of this food chain. When a plant or animal dies, decomposers break them down. The resulting nutrients enter the soil providing food for future plants to grow. So you can see how the ecosystem keeps going, recycling the nutrients by using the flow of energy.
There are many different food chains in an ecosystem. In fact, individual animal species may belong to a number of food chains. In one food chain a salmon or trout may eat a crayfish. If that same salmon eats an aquatic insect, it would belong to two food chains. All these different food chains combine to form a food web. A food web describes the many complex relationships that exist between plants and animals in an ecosystem. Every plant and animal has an important role to play.
The health of an ecosystem is often determined by the variety of different plants and animals found there. Biodiversity is a measure of the number of different species present in an ecosystem. The greater the biodiversity, the healthier the ecosystem. What do you think would happen if a species were to go extinct? Do you think the disappearance of salmon and trout from many of New England's rivers had an effect on these aquatic ecosystems?